JP3174915B2 - A method for improving the oxidative thermal stability of ethylene polymers - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to ethylene and at least one ethylene oxide in the presence of oxygen.
A method for improving the taste and odor properties and oxidative thermal stability of thermoplastic homopolymers and / or interpolymers of species comonomers. The method includes removing one or more of the remaining unreacted monomers, solvents and thermally unstable materials. The resulting polymer is also oxidatively thermally stable, having an oxidative exotherm of less than or equal to about 50% of the oxidative exotherm of the first polymer as measured by differential scanning calorimetry. This method of improving oxidative thermal stability is particularly effective for ethylene / acrylic acid interpolymers.

BACKGROUND ART Volatile components can be removed from thermoplastic polymers in various ways. One traditional method is extrusion devolatilization using an extruder equipped with a vacuum device. However, the use of vacuum alone is generally insufficient to remove residual monomers and other volatiles from the molten polymer to sufficiently improve the oxidative thermal stability of the polymer. Residual monomers and volatiles also cause odor defects in the polymer, a fact that is particularly important when the polymer is used for food storage.

U.S. Pat. No. 4,094,942 (Nakai et al.) Discloses that water or steam is blown into the nose of the mixing section of an extruder, the polymer is thoroughly mixed with water or steam, and 500 mg Hg is used.
A method is disclosed for removing unreacted monomers from the ethylene polymer during pelletization by using (absolute) or less vacuum to remove unreacted monomers and water or water vapor. Nakai et al. Teach that the products thus produced increase commercial value with respect to odor, but teach or suggest how to improve the taste performance or thermal stability of the polymer. Not.

The thermal stability of these polymers is important because they are thermally treated at elevated temperatures, especially when they are subjected to accelerated degradation and / or crosslinking in the presence of oxygen. . Oxidative thermal degradation of ethylene polymers results in gel formation and loss of physical properties (eg, extrusion coating) in the treated polymer, in addition to poor taste and odor properties from oxidative by-products formed during processing. Poor extrusion performance, such as neck-in and slow linear velocity, and reduced optical properties such as haze and gloss or color.

Antioxidants (eg, organic phosphites and hindered phenols) have been added to various polymers, including polyethylene, to improve their thermal stability. However, antioxidants have detrimental side effects, such as color formation, and they also themselves create food contact problems and lose their advantage.

Taste and odor performance and oxidative thermal stability of thermoplastic polymers are always areas of commercial demand.

DISCLOSURE OF THE INVENTION A method has been found to improve the taste and odor properties and oxidative thermal stability of thermoplastic ethylene polymers. The novel method is to remove one or more of the remaining unreacted monomers, solvents and thermally unstable substances from the first ethylene polymer and thereby measure the first ethylene polymer by differential scanning calorimetry. Forming a second more oxidatively thermally stable ethylene polymer having an oxidative exotherm of 50% or less of the oxidative exotherm of the polymer.

The novel method is particularly useful for improving the taste and odor properties and oxidative thermal stability of ethylene / acrylic acid interpolymers, which are useful for food wraps, beverage containers or spice pouches. It has a single or multi-layer laminate film structure and is widely used in the food packaging industry.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 schematically illustrates an extrusion system including two single screw operating in parallel that can be used to improve the oxidative thermal stability of an ethylene polymer.

FIG. 2 schematically illustrates a twin screw extrusion system that can be used to improve the oxidative thermal stability of an ethylene polymer.

FIG. 1 shows a cross-section of an extruder including two single screw screws useful for improving the oxidative thermal stability of an ethylene polymer, as disclosed in Comparative Examples 1-3 and Example 4 below. Shown schematically. In FIG. 1, the polymer is fed to the feed section (1) of the first extruder device (13) and is melted and conveyed into zone 1 by a screw. The temperature of the entire extruder device is controlled by a hot oil device (not shown). Ethylene (as stripping agent) is injected into zone 2 through inlet (2). The melting temperature of the first extruder is monitored by a thermocouple (3). The transfer line (4) transfers the polymer / ethylene mixture to a second extruder unit (12). Preferably, the screws of the first extruder are such that the feed to the second extruder is less than necessary to fill the screw channels (ie, the second extruder is "starved"). In addition, the rotation speed per minute (rp
m). The first inlet (5) is used to inject additional stripping agent into the polymer melt stream of the second extruder, wherein the polymer / ethylene / additional stripping agent mixture is mixed. Transported to zone (10).
The mixture of polymer / ethylene / additional stripping agent is temporarily bound by the melt seal (11) and the compression side (upstream) of the screw and is controlled in the mixing zone. The mixture of polymer / ethylene / additional stripping agent flows off the melt seal (11) and enters the first vacuum inlet area (6). A vacuum is applied to the first vacuum inlet (6) and one or more of the unreacted monomers, remaining solvent and remaining thermally unstable materials are partially devolatilized. . The polymer then enters a second compression zone where an effective melt seal is formed. The second injection inlet (7) is used to inject a second stripping agent into the polymer melt stream, immediately followed by a mixing zone (14) and a melt seal (15).
The polymer / additional stripping agent mixture is temporarily trapped between the melt seal and the compression side (upstream) of the screw to ensure proper mixing. The second vacuum port (8) is used to remove one or more of the additional unreacted monomers, residual solvent and residual thermally unstable materials, and thus has high oxidative thermal stability. Form a polymer. A melt thermocouple (9) monitors the temperature of the emerging melt stream.

FIG. 2 shows a cross-section of one screw of a co-rotating twin screw extruder useful for improving the oxidative thermal stability of ethylene polymers, as disclosed in Comparative Examples 5-7 and Example 8. Is schematically shown. In FIG. 2, the polymer is fed into the feed section (16) of a twin screw extruder device (28), melted and conveyed into zone 1 by two intermeshing screws. The temperature of each extruder zone is controlled by a temperature controller and a resistance heater (not shown). Extruder temperature is monitored by a series of thermocouples (29-36). Preferably, the feed to the extruder is
It is controlled so that it is less than necessary to fill the screw channel of the devolatilization zone (ie, the vacuum zone of the extruder is partially filled). The first inlet (17) is used to inject the first stripping agent into the polymer melt stream, and the polymer / stripping agent mixture is homogenized in the mixing zone (24) . The mixed polymer / stripping agent mixture is confined and controlled within the mixing zone by two melt seals (28, 25). The polymer / stripping mixture flows off the melt seal (25) and enters the first vacuum port region (18). A vacuum is applied to the first vacuum port (18) and is partially devolatilized, such as one or more of the unreacted monomers, remaining solvent and remaining thermally unstable materials. . A second melt seal (37) separates the first vacuum zone from the second stripping agent inlet (19). The second inlet (19) is used to inject a second stripping agent into the polymer melt stream, then immediately there is a mixing zone (33) and a melt seal (27). The mixed polymer / stripping agent mixture is temporarily confined and controlled within the mixing zone by two melt seals (37, 27). The polymer / stripping agent mixture flows off the melt seal (27) and enters the second vacuum port area (20). A second vacuum port (20) is used to remove one or more of the additional unreacted monomers, residual solvent and residual thermally unstable materials, and thus has high oxidative thermal stability. Form a polymer. A motor (not shown) drives a gear pump (21) to pump the thermally stable polymer to a pelletizer (23) and further cuts the thermally stable polymer into pellets. The liquid stream (22) cools and solidifies the polymer into pellets. The cooling liquid stream carries the cut / pelleted polymer to a separation point (not shown), and the liquid is separated from the polymer pellets and optionally recycled back through the process.

The thermoplastic ethylene polymer used in the present invention is a homopolymer or an interpolymer of ethylene and at least one comonomer such as an α-olefin or a substituted α-olefin.

Ethylene homopolymers for use in the present invention include ethylene homopolymers made using the high pressure free radical generation method and are commonly known as low density polyethylene. Low density polyethylene (LDPE), or otherwise known as high pressure polyethylene and historically as ICI type polyethylene, is a branched ethylene homopolymer made under high pressure using free radical polymerization techniques. Ethylene is polymerized randomly in the polymer chain and forms a number of branch points. The density of LDPE is governed by the degree and length of branching and is generally 0.91 per cubic centimeter.
It is in the range of -0.925 g (g / cm ³ ). LDPE has a molecular weight of AST
Indicated by the melting index (MI) measured using MD-1238 (190 ° C / 2.16 kg). LDPE used in the present invention
MI range for 0.01-1000 g / 10 min, preferably 0.1
−100.

Linear polyethylene is another type of polyethylene useful in practicing the present invention. The production of linear polyethylene is disclosed, for example, in U.S. Pat.
It includes coordination catalysts of the "Ziegler" type or of the "Philips" type, and also includes variants of the Ziegler type, such as the Natta type. These catalysts are used at very high pressures but can also (and generally) be used at very low or intermediate pressures. The products made with these coordination catalysts are generally "linear" heavy since there is substantially no branched chain of polymerized monomer units suspended from the main polymer "backbone". Also known as coalescence. Two types of linear polyethylene are also suitable for use in the present invention, they include linear high density polyethylene (HDPE) and linear low density polyethylene (LLDP).
E).

The linear high density polyethylene has a density of 0.941-0.965g / cm ^3, whereas linear low density polyethylene, 0.880
Having a density of -0.940g / cm ^3. The density of linear polyethylene is such that ethylene can be converted to a small amount of 3-20 carbons per alkene molecule, preferably 4-8 (eg 1-butene, 4-methyl 1-pentene, 1-hexene) and most preferably 1 to 4 carbons. 8 carbons per alkene molecule (ie 1-octene)
Is reduced by polymerization with an α, β-ethylenically unsaturated alkene having The amount of alkene comonomer is generally defined as a linear low-density polymer in the same density range as LDPE due to the alkyl side chains on the polymer molecule, while the polymer remains within the definition of "linear". Sufficient for coalescence density. While these polymers retain much of the strength, crystallinity, and toughness typically found in HDPE homopolymers of ethylene, high alkene comonomers have high `` cling '' and high `` cling '' in extruded or cast films. It imparts "blocking" properties and the high "slip" properties inherent to HDPE disappear.

Polymerization of ethylene into homopolymers in either solution or slurry type polymerizations, or polymers having a density of 0.94 g / cm ³ or more as specified in ASTM D-1248 (ie HDP
E polymer) to produce a copolymer having a density in the range of LDPE and medium density polyethylene (ie, LLDPE copolymer). The use of coordination type catalysts to copolymerize with higher alkenes has been variously disclosed, e.g., U.S. Pat.
Nos. 2905645, 2846625, 3089663 and 4076698. Thus, the density of the useful linear polyethylene in the present invention is a 0.88-0.965g / cm ^3.

The molecular weight of the linear polyethylene is indicated and measured by a melt index according to ASTM D-1238 condition (E) (ie 190 ° C / 2.16 kg). The melting index of the linear polyethylene useful in the present invention is 0.001 g / 10 min (g / 10 min) -1000 g / 10 min, preferably 0.01 g / 10 min-100 g / 10 min.

Ethylene can also be interpolymerized with substituted α-olefins by well known techniques. Substituted α-olefins are a well-known group of polymerizable monomers such as ethylenically unsaturated carboxylic acids, esters and anhydrides such as acrylic acid, methacrylic acid, maleic acid, maleic anhydride, methyl methacrylate. Butyl acrylate), vinyl esters of alkanoic acids (eg, vinyl acetate) and vinyl alcohol.

Interpolymers of ethylene and at least one ethylenically unsaturated carboxylic acid are particularly useful in the present invention. The term "interpolymer" means that ethylene is copolymerized with at least one comonomer. Thus, the term "interpolymer" refers to copolymers, terpolymers, and the like. These interpolymers can be made by any known technique. For example, U.S. Pat.
No. 2 (McKinney et al.) And US Pat. No. 4,248,990 (Pieski
Disclose a method for producing random and non-random interpolymers of ethylene / acrylic acid and ethylene / methacrylic acid, respectively. The amount of unsaturated carboxylic acid can vary from 0 (ie LDPE) to about 40%, depending on the carboxylic acid used for the interpolymerization. One or more ethylene / unsaturated carboxylic acid interpolymers prepared by use of a telogenic regulator as disclosed in US Pat. No. 4,988,781 are also suitable for practicing the present invention. The molecular weight of the ethylene / unsaturated carboxylic acid interpolymer is indicated by the melt index, and
D-1238 Measured under condition E (i.e. 190 ° C / 2.16 kg). The melt index of the ethylene / unsaturated carboxylic acid interpolymer is 0.1-3000 g / 10 min, preferably 1-300 g / 10 min.

Various interpolymer ionomers (eg, metal ionomers of ethylene / acrylic acid or ethylene / methacrylic acid interpolymers) are also within the scope of the invention.
U.S. Pat. No. 3,404,134 (Rees) discloses a method of, for example, crosslinking polymers to thereby produce ionomers useful in the present invention. In one embodiment of the present invention, a metal hydroxide (eg, sodium or potassium hydroxide), a nitrogen-containing base (eg, ammonium hydroxide) or a water-soluble strong base organic amine (eg, mono-, di- and trimethylamine) Is added to the devolatilizing extruder in a first injection zone and mixed with one or more interpolymers of ethylene / unsaturated carboxylic acid to effectively serve as both a stripping agent and a neutralizing / ionizing agent. Function. The water is then stripped under vacuum, thus removing one or more of the remaining unreacted monomers, solvents and thermally labile materials to form a more thermally stable ionomer.

Additives are included in the interpolymers useful in practicing the present invention, but are preferably added after the formation of the thermally stable polymer. These additives include pigments (eg, titanium dioxide), wetting agents, fillers, slip agents and anti-blocking compounds. Antioxidants are also included in the interpolymers, but they need not be effectively used in the present invention.

The solvent (or diluent) produces the ethylene polymer,
It can be used for both high pressure methods (eg, LDPE) or low pressure methods (eg, LLDPE), and is commonly used. Some of the typical solvents used during the interpolymerization include: Paraffinic hydrocarbons such as pentane, hexane, heptane, cyclohexane, branched alkanes, alkenes and alkynes (plus their various isomeric forms), or aromatic hydrocarbons such as benzene, toluene, chloro-substituted aromatic hydrocarbons such as di Chlorobenzene, or polar solvents such as alcohols, ethers, ketones and esters, or various naphtha distillates such as IS
Sold by Exxon at OPAR. These solvents are difficult to remove from the interpolymer, even after pelletization. Residual monomers (eg, ethylene and / or
Or acrylic acid) can also be retained in the interpolymer. Thermally unstable substances (e.g., free radical substances) react with oxygen causing taste problems. A thermally unstable substance as defined herein is a compound that thermally degrades in the presence of oxygen at high temperatures (i.e., the melt processing temperature of the polymer). Depending on the application, these semi-volatile components can cause taste and / or odor problems in the constructed parts made from the interpolymers, and surprisingly also cause the interpolymers to undergo oxidative heat stabilization. Reduce the nature.

Removing one or more of the unreacted monomers, solvents and thermally unstable materials remaining to form the oxidatively thermally stable interpolymer of the present invention is accomplished by all conventional means. it can.

Batch operations include equipment such as Banbury mixers or roll mills. In a batch operation, specific amounts of one or more of the polymer and the stripping agent are placed in an apparatus. The polymer is then melted and fluxed or mixed for a predetermined time. The device is evacuated periodically to devolatilize. The sample is then removed to be processed into pellets or other shapes for end use. Steam is added during this process to help devolatilize.

Continuous devolatilization is performed in a single or twin screw extruder, as shown in the examples. Other continuous devolatilizers are Bolling Mixtrumat continuous or Farr
Includes el Discpack and other types of continuous extruders, which are fitted with vacuum ports / adapters.
Many of these devices are fitted with a mixing section prior to devolatilization to improve contact of the stripping agent and the interpolymer. Devolatilization occurs by producing a thin melt that continuously regenerates new surfaces exposed to vacuum.

A particularly advantageous embodiment of the present invention for forming an oxidatively thermally stable ethylene polymer comprises the following successive steps.

(A) any stripping agent injection zone, any closed mixing zone, at least a first partially filled vacuum zone, at least a first stripping agent injection zone, at least one first closed Mixing zone,
Feeding the first ethylene polymer to an extruder that includes at least a second partially filled vacuum zone.

(B) melting the first ethylene polymer;

(C) applying a vacuum to the first partially filled vacuum zone.

(D) at least 0.1 based on all ethylene polymer raw materials
Simultaneously injecting, by weight, at least one stripping agent into the first stripping agent injection zone.

(E) mixing the stripping agent and the first ethylene polymer in a first closed mixing zone.

(F) applying a vacuum to the second partially filled vacuum zone.

(G) collecting a second more oxidatively thermally stable ethylene polymer.

Stripping agents useful in the present invention are preferably inert in the interpolymerization step. However, when forming an oxidatively thermally stable ionomer from an interpolymer of ethylene and at least one unsaturated carboxylic acid, the stripping agent must react with the unsaturated carboxylic acid. The one or more stripping agents must also have sufficient vapor pressure to either be gaseous or form gaseous bubbles under devolatilization operating conditions (ie, when the interpolymer melts). Must. Preferably, the one or more stripping agents is a light hydrocarbon (eg, ethylene, propylene or isobutane), water, steam, alcohol, carbon dioxide and / or nitrogen. Supercritical fluids (eg, supercritical carbon dioxide) are also useful as stripping agents for use in the present invention. Aqueous solutions of alkali metal hydroxides (e.g., sodium hydroxide), nitrogen-containing bases (e.g., ammonium hydroxide), water-soluble organic strong bases organic amines (e.g., mono-, di- and trimethylamines) while forming the corresponding ionomer It is particularly effective when the ethylene / unsaturated carboxylic acid interpolymer is simultaneously devolatilized. Mixtures of stripping agents are also useful in the present invention. The stripping agent has at least an oxidative exotherm of the interpolymer or ionomer.
Sufficient one of the remaining unreacted monomers to reduce by 50%
It should be used in an amount effective to remove one or more of the solvent, one or more of the solvent and the stripping agent.

The devolatilization of the interpolymer preferably comprises 1
U.S. Pat. No. 4,094,942 describes the addition of a screw using a surface renewal ratio of at least about 2 pounds per square meter or less, preferably about 1 pound per square meter or less. It is performed using a single or twin screw device with injection. More thermally stable interpolymers made using high pressure methods (eg LDPE or ethylene / acrylic acid interpolymers)
And one or more of the extruder vacuum devolatilization zones must be partially filled when the devolatilization screw is installed in line with the process (ie, prior to the pelletization process). . (I.e., the flow of the interpolymer is restricted such that the channel of the screw is partially filled.
Using a restricting device such as a slide valve or a gear pump,
Can be achieved. ) The extruder may include any stripping agent injection zone, any closed mixing zone, at least a first partially filled vacuum zone, at least a first stripping agent injection zone, at least one first closed A mixing zone, and at least a second partially filled vacuum zone. Preferably, a vacuum of 100 mmHg (absolute) or less is applied to the first vacuum zone, wherein at least one inert stripping agent is present in the first vacuum zone at a concentration of at least 0.1 wt% based on total interpolymer feed. Simultaneously injected into the stripping agent zone, and
A vacuum of 100 mmHg (absolute) or less is applied to the second vacuum zone. The stripping agent must form small gas bubbles when in the vacuum zone to effectively strip volatile interpolymers, thereby forming more oxidatively thermally stable interpolymers. No.

The screw channel of the vacuum zone is partially filled with the stripping agent / polymer mixture and is subject to frequent polymer surface renewal (ie, measured in pounds of polymer per square meter of surface) exposed to vacuum , A relatively low specific surface renewal ratio). Partially filling each vacuum zone of the extruder such that each vacuum zone has a surface renewal ratio of at least about 2 pounds per square meter or less, and preferably about 1 pound per square meter or less. Particularly effective when used in a devolatilizing extruder vacuum zone.

Partially filling the channels can be controlled in various ways, including changing the structure of the vacuum zone. This can be achieved by increasing the depth of the flight and / or simultaneously increasing the flight pitch, while increasing the number of flight starts (ie, using a multi-start screw design in the vacuum region).

The stripping agent / polymer mixture must be entrapped in order for the stripping agent and polymer to mix properly. Confinement of the stripping agent / polymer mixture can be achieved by using various means, for example, using a melt seal (ie, blister) in a single or twin screw extruder apparatus and a reverse flight in a twin screw extruder apparatus. This can be achieved by providing a high pressure compression zone along the screw, or by using axial, radial and / or transformer axial flow restrictors in a single or twin screw extruder device.

To be effective in the present invention, the devolatilization method used is such that the oxidative exotherm of the interpolymer is at least 50%.
One or more of the remaining unreacted monomer, solvent, thermally unstable material and one or more of the stripping agent must be sufficiently removed from the polymer to reduce.

The more oxidatively thermally stable polymers produced by the present invention are useful in a variety of thermoforming methods, including molding techniques (eg, injection molding, rotomolding and blow molding), film forming techniques (eg, casting, (Blow and extrusion coating) and fiber molding techniques. Oxidatively thermally stable polymers and / or ionomers have particular utility when they are used as at least one multilayer film structure having an inner layer and an outer layer, such as food packaging. Ionomers have particular utility when they are used in skin packaging.

EXAMPLES Comparative Examples 1-3 and Example 4 An ethylene / acrylic acid interpolymer having a melt index of 10 g / 10 min and an interpolymer of acrylic acid of about 10% by weight is disclosed in US Pat.
Manufactured by the technique described in US Pat. No. 4,599,392. This interpolymer was pelletized for later use in stripping experiments.

The stripping experiment was performed by loading pellets of ethylene / acrylic acid interpolymer into a first 90 mm single screw extruder with a length / diameter (L / D) ratio of 25 and a stripping agent inlet at 350 lb / hr ( 160 kg / h). This screw is
Operated according to the conditions shown in Table 1.

The molten ethylene / acrylic acid interpolymer
40 L / D, operated according to the conditions described in Table 2,
It was conveyed to a second 90 mm single screw extruder with two stripper inlets and two vacuum ports.

The screws were operated at different speeds so that the devolatilization screw was only partially filled. The second screw was provided with two inlets and two vacuum ports along its length, as shown in FIG. Each injection part of the screw itself, to close the mixing zone,
Two melt seals (ie, "Bliss Or an aperture ring). The melt seal traps the stripping agent in the area of the mixing zone and ensures that the stripping agent and the interpolymer are well mixed prior to devolatilization.

The interpolymer was extruded using the equipment described above with varying degrees of stripping and devolatilization. Table 3 describes these differences.

Differential scanning calorimetry Differential scanning calorimetry (DSC) analysis was used to determine the thermal activity of a resin sample in the presence of oxygen. For each sample, add a known amount of resin (about 5 mg) Put in a very small glass ampule. The bottom of the glass ampule was cooled with liquid nitrogen and the top of the ampule was sealed. Sealed ampoule containing resin sample at room temperature
Placed in DSC sample room. The DSC sample and reference chamber are then heated at a constant rate of 10 ° C per minute to a final temperature of 300 ° C.
I made it. The thermal activity of the sample resin was continuously monitored against a reference. The reference was an empty glass ampule. The thermal activity (ie, exotherm) of the resin sample up to 300 ° C. was calculated in joules per gram.

Analysis of Solvent The residual solvent concentration in the resin sample was measured using multiple headspace gas chromatography. For each sample, a known amount of resin (about 0.5 g) was placed in a septum sealed vial. The sample vial was then placed on an automatic headspace analyzer connected to a gas chromatography. The sample vial was then analyzed using a quantitative multiple headspace extraction method. The residual solvent concentration in the sample vial was determined from a quantitative analysis of a known solvent standard analyzed under the same multiple headspace extraction conditions.

Analysis of Residual Comonomer The concentration of residual comonomer in the resin samples was determined using solvent extraction followed by high performance liquid chromatography (HPLC) analysis. For each sample, a known amount of resin (about 0.5 g) was placed in a container with 75 mL of xylene / butanol (3: 1 ratio) extraction solvent. Seal the container,
Heated at 160 ° F. (71 ° C.) for 4 hours. Allow the container to cool,
The extraction solvent was analyzed using HPLC. In the case of acrylic acid, the concentration of acrylic acid remaining in the sample was determined from a quantitative analysis of a known acrylic acid standard.

Table 4 summarizes the melt index, total volatiles content and oxidative exotherm data of the interpolymer after processing according to the tests shown in Table 3. In Comparative Example 1-3 and Example 4, the maximum oxidative exotherm was greater than that of the original polymer (Comparative Example 1 *).
37% reduction occurred at about 240 ° C. Ethylene was not detected in all samples either before or after extrusion. The remaining comonomer for this experiment was acrylic acid.

Table 5 lists the total volatile components for the four interpolymers that were tested after the interpolymer was cut into strands and sealed for later analysis.

Comparative Examples 5-7 and Example 8 An ethylene / acrylic acid interpolymer having a melt index of 10 g / 10 min and an interpolymer of acrylic acid of 9.7% by weight was prepared by the technique described in U.S. Pat. No. 4,599,392. . This interpolymer was pelletized for later use in stripping experiments.

Combine the ethylene / acrylic acid interpolymer pellets with an L / D ratio of 33, two stripping agent inlets and two
This was done by gravity feeding at a rate of 2000 lb / hr (908 kg / hr) into a co-rotating 90 mm twin screw extruder with three vacuum ports. The screw was operated according to the conditions shown in Table 1. The twin screw device was operated according to the conditions described in Table 6.

The twin screw was provided with two inlets and two vacuum ports along its length, as shown in FIG. The first injection section of the screw itself was equipped with two melt seals (ie blisters) to close the mixing zone. The second injection section has a melt seal upstream of the vacuum port to prevent premature devolatilization of the stripping agent. Melt seals use a stripping agent in the area of the mixing zone. Ensuring that the stripping agent and interpolymer were thoroughly mixed prior to devolatilization.

The interpolymer was extruded through the above device using a metering belt feeder (not shown in FIG. 2) to ensure that the extruder was partially filled. Table 7
Describes the differences in the processing of the extruder design.

Table 8 summarizes the melt index, total volatiles content and oxidative exotherm data of the interpolymer after processing according to the tests shown in Table 7.

Table 9 lists the total volatile components of the four interpolymers tested.

The interpolymers obtained from Tests 5 *, 6 *, 7 * and 8 were, respectively, Black Clawson Extrusion Coa
Extruded and coated on paper roll raw material at a thickness of 1 mil (0.025 cm) on ter, And monitored for performance. Extrusion Coate
r had an L / D ratio of 30: 1, a 3.5 inch (8.9 cm) diameter screw and a 30 inch coat hanger die. The processing temperature was 550 degrees Fahrenheit (288 ° C) and the screw speed was 85 revolutions per minute (RPM). The cooling roll is
Operated at 440 feet (134 m) per minute for neck-in measurements. To measure the maximum linear speed, the chill roll speed was increased until the web started pinching each side of the die. These data are shown in Table 10.

These data show that the more oxidatively thermally stable interpolymers treated according to the present invention exhibit the same neck-in and linear velocity performance, if not better, than that of the base interpolymer.

Film Generation Method for Taste and Odor Evaluation Cast films were made from Example 5 * and Example 8. Cast films were made in small cast film units. The extruder had a 1.5 inch (3.8 cm) diameter screw and a 20: 1 L / D. The cast film unit had a 12 inch (30 cm) slot die. The film was produced at a temperature of 550 degrees F (288 degrees C). The production conditions used result in a 1 mil (0.025 mm) cast film.

Odor Evaluation Method For each sample, 10 g of cast film was placed in a 16 oz (473 mL) glass container. These containers are
Sealed and placed in oven at 60 ° C. for 16 hours. The sample was taken out and allowed to cool. Sample headspace odors were then compared using a panel of test panelists. Panelists were required to select a preferred sample (ie, preferred) and recorded the results.

Taste evaluation method For each sample, 20 g of casting film was placed in a glass container together with 800 mL of drinking water. The container was then sealed and placed in an oven set at 60 ° C. for 16 hours. The sample was then removed and allowed to cool. The water from each sample was split into portions and tasted by test panelists. Panelists were required to select a preferred sample (ie, preferred) and recorded the results.

Taste and odor results Taste and odor results from the cast film evaluations are summarized in Tables 11 and 12, respectively.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-2-194004 (JP, A) JP-A-52-49267 (JP, A) JP-A-51-11882 (JP, A) 239705 (JP, A) JP-A-51-64587 (JP, A) JP-A-59-202205 (JP, A) JP-A-58-147332 (JP, A) (58) Fields investigated (Int. ⁷ , DB name) C08F 6/00-6/28

Claims (10)

(57) [Claims] (A) optionally present stripping agent injection zone, optionally present closed mixing zone, at least a first partially filled vacuum zone, at least a first stripping agent injection zone; Feeding a first ethylene polymer to an extruder comprising at least one first closed mixing zone, at least a second partially filled vacuum zone, (b) melting the first ethylene polymer (C) applying a vacuum to the first partially filled vacuum zone; (d) at least 0.1 based on the total ethylene polymer feedstock.
Simultaneously injecting by weight at least one stripping agent into the first stripping agent injection zone; (e) mixing the stripping agent and the first ethylene polymer in the first closed mixing zone (F) applying a vacuum to a second partially filled vacuum zone; and (g) harvesting a second, more oxidatively thermally stable ethylene polymer. A method for improving the taste and odor properties and oxidative thermal stability of a first thermoplastic ethylene polymer. 2. The oxidative exotherm of the second ethylene polymer obtained in step (g) having an oxidative exotherm of 50% or less of the oxidative exotherm of the first polymer as measured by differential scanning calorimetry. The method of claim 1 wherein the ethylene polymer is a thermally stable ethylene polymer. 3. The process of claim 1 wherein step (a) is immediately after the ethylene homopolymerization reaction. 4. The method of claim 1 wherein step (a) is immediately after the interpolymerization reaction of ethylene with at least one other comonomer. 5. The method according to claim 4, wherein the comonomer is acrylic acid or methacrylic acid. 6. The method of claim 1 wherein each vacuum zone of the extruder has a specific surface renewal ratio of less than 2 pounds per square meter. 7. The stripping agent comprises a light hydrocarbon, water,
The method according to claim 5, wherein the method is at least one selected from the group consisting of an aqueous solution of a metal hydroxide, a nitrogen-containing base, a water-soluble organic strong base, an organic amine, steam, an alcohol, carbon dioxide, and nitrogen. 8. The method of claim 7 wherein the stripping agent is an aqueous solution of sodium hydroxide, thereby further forming an oxidatively thermally stable ionomer. 9. An ionomer produced by the method of claim 8. 10. A multilayer film structure having an inner layer and an outer layer, at least one of which comprises the ionomer of claim 9.